Anode containing pin-type inserts

ABSTRACT

An anode for use in a cathodic protection system or other electrolytic process includes a body of lead or a lead alloy and a plurality of pins or wire inserts of tantalum, titanium, niobium, zirconium, vanadium or a similar metal coated with a thin outer coating of platinum or other noble metal from Group VIII of the Periodic Table. The inserts will normally range from about 50 to about 250 mils in diameter and the coating will generally be from about 1 to about 10,000 microinches in thickness.

United States Patent [191 Benedict [451 Oct. 29, 1974 ANODE CONTAININGPIN-TYPE INSERTS [.75] Inventor: Risque L. Benedict, Santa Monica,

Calif.

[73] Assignee: Esso Production Research Company,

Houston, Tex.

[22] Filed: Dec. 18, 1972 [21] Appl. No.: 315,768

[52] U.S. Cl 204/196, 204/280, 204/288, 204/289, 204/290 F, 204/292 [51]Int. Cl. C23f 13/06, B011: 3/06 [58] Field of Search 204/280, 293, 196,197, 204/288, 289, 292

[56] References Cited UNITED STATES PATENTS 3/1960 Newell et al. 204/290R 3/1963 Preiser et a1 204/196 3,108,939 10/1963 Sabins 204/196 FOREIGNPATENTS OR APPLICATIONS 1,047,030 11/1966 Great Britain 204/292 PrimaryExaminerF. C. Edmundson Attorney, Agent, or Firm-.lames E. Reed [5 7]ABSTRACT An anode for use in a cathodic protection system or otherelectrolytic process includes a body of lead or a lead alloy and aplurality of pins or wire inserts of tantalum, titanium, niobium,zirconium, vanadium or a similar metal coated with a thin outer coatingof platinum or other noble metal from Group VIII of the Periodic Table.The inserts will normally range from about 50 to about 250 mils indiameter and the coating will generally 'be from about 1 to about 10,000microinches in thickness.

10 Claims, 6 Drawing Figures BACKGROUND OF THE INVENTION 1. Field of theInvention This invention relates to anodes for use in impressed currentcathodic protection systems and other electrolytic processes and isparticularly concerned with leadtype anodes containing wire or pininserts.

2. Description of the Prior Art Lead and lead alloy anodes used inimpressed current cathodic protection systems and similar electrolyticprocesses tend to deteriorate in the presence of brines. Thisdeterioration is manifested by' the formation of coatings of leadchloride and other salts which eventually deactivate the anodes andprevent further electrolytic action. It is known that this difficultycan be alleviated by providing such anodes with small pins or inserts ofplatinum which will serve as nucleation sites and promote the formationof lead peroxide in lieu of lead chloride and other undesirable divalentsalts. The improvements which can be obtained in this manner are SUMMARYOF THE INVENTION The present invention provides an improved leadv typeanode for use in impressed current cathodic protection systems andsimilar electrolytic processes which at least in part eliminates thedifficulties outlined above. This improved anode comprises a lead metalanode body and a plurality of pins or wire inserts extending into theanode body at spaced intervals over the outer surface thereof. Thesepins or inserts are made of tantalum, titanium, niobium, zirconium,vanadium or an alloy containing one or more ofthese metals as theprincipal constituent and are coated with a thin outer coating ofplatinum or a similar noble metal from Group VIII of the Periodic Table.It has been found that these noble metals have surprisingly lowdeterioration or attrition rates when used on coated pins or inserts inlead metal anodes and that a plurality of such inserts can be used toreduce the deterioration rates of such anodes to a value of one-tenth orless that normally obtained with anodes containing conventional platinumpins or inserts. A conventional anode containing three platinum insertsper square foot, for example, may have a useful life of about 6 years;whereas an anode containing of the coated pins of this invention persquare foot may have a useful life of 50 years. This makes possiblesignificant improvements in impressed current cathodic protectionsystems and other electrolytic processes without substantial increasesin cost.

The pins or inserts used in the improved anodes of the invention willnormally have diameters of from about 50 to about 250 mils and will beprovided with coatings of platinum or a similar noble metal between land about 10,000 microinches in thickness. This use of relatively largecoated pins or inserts facilitates driving of the inserts into the anodebodies, permits the use of longer inserts, and makes the coated insertsmore difficult to dislodge than the smaller diameter platinum insertsgenerally employed heretofore. It is preferred that the inserts extendthrough the anode body so that fresh platinum is continually exposed asthe lead metal deteriorates and that the unexposed end of each insert besecured to increase the resistance to forces generated by the formationof lead peroxide which tend to extract the inserts from the anode body.These and other features of the improved anodes responsible for theirimproved performance will be described in detail hereafter.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 in the drawing depicts oneembodiment of the improved anode of the invention which is particularlyadapted for use on offshore drilling and production platforms and othermarine installations;

FIG. 2 is an enlarged cross section of the anode of FIG. 1 taken aboutthe line 22;

FIG. 3 illustrates an alternate embodiment of the invention which may beused on ships, underwater storage tanks, and similar marine structures;

FIG. 4 is a cross sectional view of the anode of FIG. 3 taken about theline 4-4;

FIG. 5 illustrates still another embodiment of the invention which maybe employed in impressed current cathodic protection systems and otherelectrolytic processes; and,

FIG. 6 is a cross sectional view of the anode of FIG. 5 taken about theline 6-6.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The anode depicted in FIG. 1 ofthe drawing comprises a cylindrical lead metal anode body 11 which issuspended by means of an insulated terminal member 12 and an insulatedelectrical conductor 13. The anode body may be made of metallic lead butwill normally be composed of a lead alloy containing small amounts ofsilver, antimony, tellurium, bismuth and other metals. Experience hasshown that alloys of this type generally less prone than metallic leadto form lead chloride in the presence of chloride ions and are thereforesomewhat more effective for use as anodes in electrolytic processes. Thepreferred alloys will normally contain up to about 5 percent silver andup to about 10 percent antimony. Typical alloy compositions which may beused include the following: (a) lead-98 percent, silver- Zpercent; (b)lead-99.5 percent, antimony-0.5 percent; (c) lead-93 percent, silver-lpercent, antimony-6 percent; (d) lead-97.5 percent, silver-2 percent,tellurium- 0.3 percent, bismuth-0.2 percent; (e) lead-96 percent,sliver-2 percent, antimony-1.5 percent, copper-0.4 percent,tellurium-0.l percent; and (f) lead-99.8 percent, tellurium-0.l percent,bismuth 0.1 percent. All of these compositions may include othermaterials present in small amounts as impurities. A variety of otherlead alloys suitable for use as anodes after treatment to provide asurface coating of lead peroxide have been described in the literatureand will be familiar to those skilled in the art.

The anode body 11 is providedwith a plurality of pins or wire inserts 14which are spaced at regular intervals over the outer surface of thebody. Each of these pins or inserts is made of tantalum, titanium,niobium, zirconium, vanadium or an alloy containing one or more of thesemetals as the principal constituent and is coated with a thin outercoating of platinum or a similar noble metal from Group Vlll of thePeriodic Table. The use of titanium inserts coated with a layer ofplatinum or a platinum-iridium alloy between about 1 and about 10,000microinches in thickness is generally preferred. These inserts willnormally be between about 50 and about 250 mils in diameter and will bespaced to provide from about 5 to about 50 or more inserts per squarefoot of anode surface area. As shown more clearly in FIG. 2, each insertpreferably extends through the wall of the lead body and if desired maybe provided with circumferential, longitudinal, or spiral ridges to aidin holding it in place.

The inserts used in the anode body are positioned by drilling holes inthe body at the desired locations and then .driving the inserts intoplace. In general, these holes should extend normal to the outer surfaceof the body and be small enough to insure a very tight ftt. Otherwise,the formation of a thick layer of lead peroxide on the surface of thebody may result in the inserts being pulled out of electrical contactwith the lead alloy anode so that no further nucleation of lead peroxidecan take place. This will in turn accelerate deterioration of the anodebody, in some cases perhaps by a factor of as much as 100 times.

The relatively large coated pins or inserts used for purposes of theinvention can be driven to much greater depths and are considerably moredifficult to dislodge from the anode body than the platinum inserts usedin the past. This is due in part to the greater rigidity of therelatively large coated inserts. The flexural rigidity of such an insertis a function of the modulus of elasticity of the metal employed and themoment of inertia of the cross sectional area about the transverse axis.Although the modulus of elasticity of platinum is slightly higher thanthat of titanium for example, the cost of platinum is such that the useof platinum inserts greater than about 50 mils in diameter isprohibitively expensive. Titanium inserts coated with l microinch ofplatinum cost about l/l00 as much as platinum inserts of the same sizeand hence the use of coated inserts with considerably greater diametersthan those of the platinum inserts employed heretofore is feasible. Themoment of inertia of an insert increases as the fourth power of thediameter, so that doubling the diameter will increase the flexuralrigidity by a factor of 16. The flexural rigidities of conventionalplatinum inserts and typical coated inserts employed for purposes of theinvention are set forth below.

Modulus of Flexural Type of lnsert Elasticity Rigidity Hard DrawnPlatinum-50 mils Diameter 22.6 X 10 6.95 Annealed Tantalum-I00 milsDiameter 27.0 X It) l33 Wrought Niobium-I00 mils Diameter l5.() X IOl 74Titanium-I00 mils Diameter 16.8 lO" 83 tional to the area of contact.The area of contact is a linear function of the wire insert diameter andof its length. The force exerted on the insert due to the formation oflead peroxide on the lead anode surface is also proportional to theinsert diameter and thus the net resistance to withdrawal of the insertfrom the anode depends upon the distance to which it is driven. The useof the coated inserts of the invention makes possible useful anode livesmany times those that can be obtained with conventional lead anodescontaining relatively short platinum inserts.

As pointed out earlier, it is preferred that each of the coated insertsbe driven completely through the lead anode. Where the inner surface ofthe lead is not exposed, the inner end of each insert can be bent at aright angle to aid in holding the insert in place. The increasedflexural rigidity of the relatively large coated inserts makes theseinserts much more difficult to dislodge from the anode than conventionalplatinum inserts. Before an insert which is bent at the inner end asdescribed above can be pulled out of the lead anode, the inner end mustbe straightened out by bending it through an angle of about The maximumbending or deflection which takes place under a given force is aninverse function of the flexural rigidity of the insert and hencedoubling the insert diameter will reduce by a factor of 16 the amount ofbending or deflection that takes place. By using relatively large coatedinserts, the danger of losing the inserts before substantially all ofthe lead is consumed can be minimized.

The entire length of each of the wire inserts is substantially coveredwith platinum or a similar noble metal. Tests in both the laboratory andfield have shown that platinum and platinum alloys generally havedeterioration rates of about 6 milligrams per ampere year when used asanodes in the conventional fashion but that such metals have negligibleattrition rates of less than 1 milligram per ampere year when employedon coated inserts in accordance with the invention. Because there isthus virtually no loss of platinum or other noble metal from theinserts, coatings of as little as l microinch in thickness are feasible.As the lead surrounding each of the inserts deteriorates, new platinumis constantly being uncovered and exposed to the electrolyte in thesystem. In the event that the anode falls into the mud bottom where therate of anode deterioration will be much higher than in a circulatingaqueous environment, the exposed platinum may be destroyed. The exposureof fresh platinum after the anode is returned to the aqueousenvironment, however, will result in a return of the anode to the formerlow deterioration rate.

The dimensions and configuration of the anode will depend primarily uponthe structure to be protected and the period over which effectiveprotection is required. As pointed out earlier, the improved anodes ofthe invention are considerably less expensive than conventional leadtype anodes containing platinum inserts or microanodes and permit theuse of a much greater number of inserts than has generally beenconsidered feasible heretofore. This use of more inserts results in alonger lasting anode, permits operation of the anode at higher currentdensities, and for a given life expectancy makes possible the use of asmaller diameter anode. The ability of the improved anodes to operate athigher current densities is particularly important because of the highinitial current densities required for the effective protection of steelin sea water. The use of a smaller diameter anode for a given lifeexpectancy results in savings in anode costs, simplifies suspensiontechniques, and makes the anodes more readily retrievable.

FIGS. 3 and 4 in the drawing illustrate an alternate embodiment of theimproved anode of the invention which is intended for use on ships,underwater storage tanks and similar structures. The anode shown inFIGS. 3 and 4 comprises a lead or lead alloy anode body which is mountedupon a dielectric backing member 21 and held in place by a gasket 22 andan apertured fixture or bracket 23, both made of polyvinylchloride,polychloroprene, fiberglass reinforced polyester and epoxy mastics orother suitable dielectric material. The portion of the anode bodyexposed by the apertured fixture is provided with a plurality of coatedwire inserts 24. Each insert includes an inner core of tantalum,titanium, niobium, zirconium, vanadium or an alloy containing one ofthese metals as the principal constituent and a thin outer coating ofplatinum or a similar noble metal from Group Vlll of the Periodic Table.The inserts are preferably between about 100 and about 250 mils indiameter and are spaced to provide between about 5 and about 50 or moreinserts per square foot of anode surface. As indicated in FIG. 4, eachinsert extends through the lead metal anode body and is bent overparallel to the back of the body as indicated by reference numeral 25.This aids in resisting forces generated by the formation of leadperoxide on the exposed surface of the anode which may otherwise tend topull the insert from the anode. The anode assembly will normally bemounted on a dielectric shield on the surface of the member to beprotected. it is generally preferred that this shield extend for adistance of 10 feet or more beyond the anode in all directions. Thedielectric shield may comprise a coating of coal tar epoxy resin,phenolic epoxy resin, epoxy mastics fiberglass reinforced polyestermaterial, polyurethane, polyvinylchloride, neoprene rubber or otherdielectric ma terial and may be applied by spraying, baking, wrapping,or other conventional technique. The anode as sembly may be mechanicallymounted on the surface to be protected by means of countersunk brassscrews which extend through holes 26 in the assembly and are coveredwith polychloroprene putty or similar dielectric material. Othermounting techniques may also be used. Current will normally be suppliedto the backside of the anode in the conventional manner by means of aconductor which extends through an opening in the hull or other surfaceon which the assembly is mounted and is connected to the anode body.

Still another embodiment of the invention is shown in FIGS. 5 and 6ofthe drawing. This embodiment comprises an elongated hollow anode body30 of lead or a lead alloy which is filled with an inner core of epoxyresin or similar material 311. An insulated cap or terminal member 32provided with insulated electrical conductor 33 is attached to the upperend of the anode body. Coated inserts 34 of platinum coated titanium,tantalum, or niobium are positioned in the anode body at regularlyspaced intervals over its surface. These inserts extend into the openingin the lead or lead alloy body and are bent over before the opening isfilled with the epoxy resin. This aids in resisting forces due to theformation of lead peroxide which tend to dislodge the inserts. in lieuof using an epoxy resin core, a close fitting rod of titanium, tantalum,niobium or similar metal can be driven into the opening in the bodyafter the inserts have been placed in order to bend them over andprovide the body with greater strength. The outer ends of the insertsare substantially flush with the outer surface of the anode body. Anodesof this type are useful in a variety of electrolytic processes usinglead type anodes.

it will be apparent from the foregoing that the im proved anodes of theinvention can be constructed in a variety of different configurations.Regardless of the particular configuration used, the coated pins orinserts provide significantly longer anode life, permit operation athigher current densities, and for a given anode life make feasible theuse of smaller anodes than do the platinum inserts or microelectrodesemployed heretofore.

l claim:

it. An anode for a cathodic protection system or similar electrolyticprocess which comprises a lead metal anode body; a plurality of pinsextending into said body from the outer surface thereof, said pins beingmade of a base metal selected from the group consisting of tantalum,titanium, niobium, zirconium, vanadium and alloys thereof and beingcoated with a noble metal from Group Vlll of the Periodic Table; andmeans for applying an electric current to said anode body.

2. An anode as defined by claim 1 wherein said noble metal is platinum.

3. An anode as defined by claim 1 wherein said lead metal is-alead-silver alloy containing up to about 5 percent silver by weight.

4. An anode as defined by claim 1 wherein said lead metal is alead-antimony alloy containing up to about 10 percent antimony byweight.

5. An anode as defined by claim 1 wherein said pins have diametersbetween about 50 and about 250 microinches.

6. An anode as defined by claim 1 wherein the thickness of the noblemetal coating on said pins is between 1 and 10,000 mils.

7. An anode as defined by claim ll containing from about five to about50 coated pins per square foot of exposed anode body surface area.

8. An anode as defined by claim 1 wherein each of said pins is providedwith ridges.

9. An anode for a cathodic protection system or similar electrolyticprocess which comprises a lead metal anode body; a plurality of pinsextending from the outer surface of said anode body completely throughsaid anode body; said pins being made of a base metal selected from thegroup consisting of tantalum, titanium, niobium, zirconium, vanadium andalloys thereof and being coated with a noble metal from Group VIII ofthe Periodic Table; and means for applying an electric current to saidanode body.

10. An anode as defined by claim 9 wherein theinner ends of said pinsextend beyond the inner surface of said anode body and are bent overadjacent said surface.

1. AN ANODE FOR A CATHODIC PROTECTION SYSTEM OR SIMILAR ELECTROLYTICPROCESS WHICH COMPRISES A LEAD METAL ANODE BODY; A PLURALITY OF PINSEXTENDING INTO SAID BODY FROM THE OUTER SURFACE THEROF, SAID PINS BEINGMADE OF A BASE METAL SELECTED FROM THE GROUP CONSISTING OF TANTALUM,TITANIUM, NIOBIUM, ZIRCONIUM, VANADIUM AND ALLOYS THEREOF AND BEINGCOATED WITH A NOBLE METAL FROM GROUP VIII OF THE PERIODIC TABLE; ANDMEANS FOR APPLYING AN ELECTRIC CURRENT TO SAID ANODE BODY.
 2. AN anodeas defined by claim 1 wherein said noble metal is platinum.
 3. An anodeas defined by claim 1 wherein said lead metal is a lead-silver alloycontaining up to about 5 percent silver by weight.
 4. An anode asdefined by claim 1 wherein said lead metal is a lead-antimony alloycontaining up to about 10 percent antimony by weight.
 5. An anode asdefined by claim 1 wherein said pins have diameters between about 50 andabout 250 microinches.
 6. An anode as defined by claim 1 wherein thethickness of the noble metal coating on said pins is between 1 and10,000 mils.
 7. An anode as defined by claim 1 containing from aboutfive to about 50 coated pins per square foot of exposed anode bodysurface area.
 8. An anode as defined by claim 1 wherein each of saidpins is provided with ridges.
 9. An anode for a cathodic protectionsystem or similar electrolytic process which comprises a lead metalanode body; a plurality of pins extending from the outer surface of saidanode body completely through said anode body; said pins being made of abase metal selected from the group consisting of tantalum, titanium,niobium, zirconium, vanadium and alloys thereof and being coated with anoble metal from Group VIII of the Periodic Table; and means forapplying an electric current to said anode body.
 10. An anode as definedby claim 9 wherein the inner ends of said pins extend beyond the innersurface of said anode body and are bent over adjacent said surface.